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Malvo is one of two men convicted for a string of shootings that terrorized the Washington, D.C., area in the fall of 2002, when Malvo was 17. Ten people died and three were wounded.

Malvo is serving life without parole. Public defender James Johnston argued the sentence is illegal because the U.S. Supreme Court determined such sentences are unconstitutional for juveniles. In 2012, the Supreme Court struck down life sentences without parole for juveniles. In 2016, it said that holding applied retroactively to cases on appeal.

As WTOP was first to report, federal district court judge Raymond Jackson ruled Friday that because of those two Supreme Court decisions, Malvo must be resentenced, Williams reported.

"We are reviewing the decision and will do everything possible, including a possible appeal, to make sure this convicted mass murderer serves the life sentences that were originally imposed," said Michael K. Kelly of the Virginia Office of the Attorney General.

John Allen Muhammad, the other man convicted in the sniper shootings, was executed in Virginia in 2009.

Malvo was first put on trial in Chesapeake, Virginia, in 2003, in a trial that was moved from Fairfax County. He was convicted of capital murder. The jury only had the option of a death penalty or life in prison without parole and opted for a life sentence.